What is Newton’s First Law of Motion?
Due to the mass of the car, the child has to apply a large force to move the car.
Newton’s first law of motion is about inertia. While this might sound technical, it’s not.
Inertia is a characteristic of an object’s state of motion.
Well, this doesn’t sound very easy, so let me try again. Actually, I am writing this so that a special technical reviewer, Stanley (4th grader), will give me a stamp of approval. Stanley has agreed to review this article, and I want it to be scientifically correct and easy to understand.
Inertia is a how much a stationary object resists any change in its motion. As long as all the forces acting on an object are balanced, the object does not move. Thus only an unbalanced force can move a stationary object. The amount of force needed depends on the object’s inertia.
An unbalanced force applied to the car changes it state of motion.
Inertia is a how much a moving object resists any change in its motion, such as a change in direction, increasing or decreasing its speed or stopping it.
Now here is the part that sounds a bit “goofy” to us because it never happens because of friction. But IF there were no unbalanced forces action on a thrown baseball (no gravity and no friction) the ball would continue to move in the same direction at the same speed for ever and ever.
NOTE the big IF. The problem for us is that we live on Earth that has gravity, which is a force that pulls everything on Earth in a downward direction in a straight line pointing toward the center of Earth. On Earth there is friction, which is any force that acting against the motion of an object. On Earth, air acts as a frictional force when things move through it.
Summary
1. Stationary objects with more inertia are more difficult to move.
Stationary objects with more inertia have more mass.
2. Moving objects with more inertia are more difficult to stop.
Moving objects with more inertia have more mass.
While inertia and mass are proportional, they are not equal.
Now about using inertia to measure the mass. This would be done by using an inertia balance, see Inertia vs. Mass for instructions to make your own inertia balance.
The video gives a more detailed explanation of inertia, balanced, and unbalanced forces.
